Disk array data storage systems have multiple storage disk drive devices which are arranged and coordinated to form a single mass storage system. The disk array has multiple mechanical bays or interfacing slots which receive individual storage disks. The memory capacity of such a storage system can be expanded by adding more disks to the system, or by exchanging existing disks for larger capacity disks.
Some conventional disk array data storage systems permit a user to connect or "hot plug" additional storage disks to available interfacing slots while the system is in operation. Although the "hot plug" feature is convenient from a user standpoint, it presents some difficult control problems for the data storage system. One problem that arises during "hot plug" occurs when a user attempts to switch storage disks among the various interfacing slots. For instance, a user might remove the disk that was in one interfacing slot and plug it into another interfacing slot. When this occurs, the conventional disk array system writes data to the incorrect storage disk. The prior art solution to this problem has been to simply place a limitation on the user not to shuffle the storage disks among interfacing slots. Thus, once a storage disk is assigned to a slot, it remains there.
Another problem concerns the processing of I/O requests during removal of a storage disk from the disk array. When the storage disk is decoupled from the interfacing slot, conventional storage systems typically return a "timeout" warning, indicating that the I/O request has failed. This warning is usually generated when the storage system can not access an existing storage disk due to mechanical or other storage problems. Here, in contrast, the reason for the failed access is that the storage disk is missing. A more appropriate interpretation, then, is to report that the storage disk has been removed, not that the I/O request has failed. It would be helpful if a disk array could distinguish between a missing storage disk and a failed I/O request to an existing storage disk.
Another problem facing large disk array data storage systems having many independent storage disks concerns the effect that attachment or detachment of a storage disk has on the rest of the storage disks coupled to the system. In present disk arrays, attachment or removal of a storage disk causes a temporary halt of all I/O activity to all storage disks on the disk array. It would be advantageous to construct a disk array that identifies the storage disk that has been attached or removed and to isolate I/O activity involving that storage disk from other I/O's, thus enabling the remaining storage disks to continue activity.